Such sensing elements may be designed as gas sensors for determining the concentration of a gas component of a gas mixture, in particular the oxygen concentration in the exhaust gas of an internal combustion engine, or as sensor for measuring the temperature or the pressure of the gas mixture, in particular the temperature or the pressure of the exhaust gas of an internal combustion engine.
In a known gas sensing element, in particular for determining the oxygen concentration of the exhaust gas of internal combustion engines (German Published Patent Application No. 41 26 378), the elastic, plug-type molded piece that is used to feed the connector cable out of the housing in a gas-tight manner is made of a heat-resistant material such as PTFE. However, materials such as silicon rubber or fluorelastomers, for instance FKM or FFKM, are used as well. By radial compression of the molded piece, which is brought about by an all-around tamping of the housing, the molded piece is pressed onto the insulation covering of the cable and then has a sealing effect; the sealing effect may be optimized further by the shape of the axial feed-through hole for the cable and by the surface roughness of the insulation covering of the cable.
Under temperature load, the characteristics of the elastomers exposed to mechanical pressure change in a disadvantageous manner with respect to the sealing effect. Depending on the type of elastomer used, it will soften or harden, the hardening even leading to embrittlement in extreme cases. An adequate sealing effect will then no longer be ensured in all these cases. As a result, in sensing elements where higher thermal demands are made on the cable exit, the use of elastomeric molded pieces has already been abandoned and other measures are taken to seal the cable exit point.